In the related art, a valve timing adjustment apparatus adjusts a relative phase (hereinafter, referred to as a “rotor-to-rotor phase”) between first and second rotors. The first and second rotors are coupled with a crank shaft and a cam shaft through a planetary motion of a geared rotor and respectively rotate.
In a type of the apparatus disclosed in JP 4442574 B, a planetary carrier supports the geared rotor from the inside in a radial direction, which meshes with a first gear portion of the first rotor and a second gear portion of the second rotor. In particular, the first rotor is supported from the outside in the radial direction by ball bearing rollers which are mounted on the second rotor to interpose the first rotor on both sides in an axial direction. As a result, the planetary carrier is tilted relative to the axial direction within a range of an internal clearance of the bearing.
In the apparatus disclosed in JP 4442574 B, the planetary carrier receives a radial load in a first region that is offset in the axial direction to one end from a center position, and the planetary carrier is supported by the ball bearing rollers in a second region that is offset to the other end from the center position. Accordingly, when the planetary carrier receives the radial load in the first region, the planetary carrier is tilted around a specific point as a center point in the second region. The geared rotor supported by the planetary carrier is tilted together with the planetary carrier, and thus the geared rotor undergoes increasing wear due to gear rattle occurring at locations at which the geared rotor meshes with the first and the second gear portions. Accordingly, from the viewpoint of durability the amount of tilt is required to be regulated.
Herein, in the ball bearing roller of the apparatus disclosed in JP 4442574 B, a plurality of rolling elements arranged in two rows are installed between an outer ring mounted on the second rotor and an inner ring that supports the planetary carrier. With the plurality of rows of rolling elements, when the inner ring and the planetary carrier is tilted relative to the axial direction, the tilting of the inner ring is received by the outer ring through each rolling element in two circumferences that are apart in the axial direction from each other. Effects of tilt regulation by the stop structure become great. However, since either a total contact area between the outer ring and the entirety of the rolling elements or a total contact area between the inner ring and the entirety of the rolling elements becomes large, a contact pressure occurs in a large area of a contact interface when the tilt is regulated. As a result, wear increases in the ball bearing roller, the inner ring of which is tilted, thereby causing a reduced lifespan and reduced durability.